Electric lamp for picture projection



May 6, 1941.. E. MAY

ELECTRIC LAMP FOR PICTURE PROJECTIOS Filed June' 14, 1939 INVENTOR Patented May 6, 1941 ELECTRIC LAMP FOR PICTURE PROJECTION Erwin May, Wetzlar, Germany, assignor, by mesne assignments, to Frank Dumur, Lausanne, Switzerland Application June 14, 1939, Serial No. 279,102 In Germany June 20, 1938 1 Claim.

This invention relates to improvements in electric lamps for picture projection apparatus in which the image of the lamp filament is refiected by means of a concave mirror and directed towards the object, for instance a film which is exposed through a film Window in the plane of which the enlarged image of the filament is formed.

In order to obtain an evenly illuminated area it has been proposed to arrange the filament in the lamp in the form of parallel threads in a single plane and then employ optical means, such as a ringformed mirror, to produce a laterally displaced reflected image of the filaments in their own plane in the spaces between the illament threads. The filament is reflected from a central point in a said concave mirror and the image of the filament is formed enlarged in the plane of the film window.

However, the closer said central mirror point is moved to the edge of the mirror, the smaller becomes the image of the filament in the film window. In addition, the images of the individual filament threads appearing between the real filament threads are darker because the image forming rays pass twice through the lamp bulb and [because the said ring formed mirror has materially less reflecting surface.

It has also been proposed to arrange the filament threads in two parallel rows with the threads in staggered relation. This arrangement does not result in an evenly illuminated area because the spaces between the filament threads are not filled out but can be caught by the light rays. As a consequence even such rays which do not pass through the lamp b ulb become more sensitive to the irregularities in the illuminated area caused by the spaces between the filament threads. In neither case it is possible to provide an evenly illuminated area.

The object of this invention is to provide a lamp filament in which the filament threads are so arranged as to eliminate the disadvantages mentioned above. The invention is embodied in a filament comprising two parallel rows of threads in two planes perpendicular to the optical axis of the system and in which the threads in the one row are alined with the threads in the other row and not staggered. This arrange-- ment embodies the advantage that a practically even intensity of light is obtained for all the points in the concave mirror from which the light is reflected except for those points which lie within a space in the mirror which is equal in dimension to the size of the lamp bulb. By appropriate spacing of the filament threads, the range of the angles, under which the image of the filament is reflected from different points in the concave mirror, may be kept within narrow limits whereby to insure an even illumination at the film window.

In the drawing accompanying this specification and illustrating the invention Fig. 1 is a diagrammatic view illustrating the arrangement of the filaments according to this invention, the filaments being arranged in wo planes at right angles, one of said planes being parallel to the optical axis of the system.

Fig. 2 is a diagram illustrating the illuminating projection system according to this invention.

In Fig. 1 there are shown a filament consisting of four threads 5, 5 and 6, 6. The optical axis of the system is marked 1. The threads are arranged in parallel planes at right angles to the axis 1, and each pair of threads 5, 5 is also in a plane parallel to said axis. The spaces 8 between the threads are not covered by a thread in the other row but are free. This space however, is viewable only within an area which lies within the lines 9 and I0 and which does not assist materially in illuminating the film window.

Fig. 2 illustrates diagrammatically a projection system which includes the electric lamp l5 having the filament threads arranged according to Fig. 1. The reflecting mirror is indicated at It and the film window at [1. It will be seen that the image of the filament at l8 which is formed by reflection from a point l9 near the center of the mirror is of the same size as the image formed by reflection from another point 20 near the edge of the mirror. The film window is therefore evenly illuminated.

In connection with Fig. 1 it will be noticed that the spaces 8 are also viewable to the right of the line 35. However as seen in Fig. 3 this line indicates the limit of the angle of reflection of the mirror l6 and such viewing of said spaces is therefore of no consequence.

I claim:

An incandescent lamp for picture projection purposes having a filament consisting of four spaced parallel filament threads arranged in two planes parallel to the projection axis of the lamp, said planes being spaced equidistantly from said axis, the threads in one plane being alined with the threads in the other plane across said axis, the spaces between all of the threads being unobstructed, said threads being of such diameter and so placed in relation to each other and to the projection axis of the lamp that the unobstructed space between said threads along said axis is less than the diameter of the threads whereby to increase the efiective light intensity of said lamp.

ERWIN MAY. 

